Re: [Qemu-devel] [PATCH 6/6] hw/arm/boot: enable DTB support when booting ELF images

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 9 September 2014 20:08, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 5 September 2014 16:15, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> Add support for loading DTB images when booting ELF images via -kernel.
>> The DTB image is located at the next 4 KB boundary above the highest address
>> covered by the loaded ELF image.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  hw/arm/boot.c | 18 ++++++++++++++++--
>>  1 file changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
>> index 8d8653978dfe..60c4f6af7884 100644
>> --- a/hw/arm/boot.c
>> +++ b/hw/arm/boot.c
>> @@ -458,7 +458,7 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
>>      int kernel_size;
>>      int initrd_size;
>>      int is_linux = 0;
>> -    uint64_t elf_entry;
>> +    uint64_t elf_entry, elf_low_addr;
>>      int elf_machine;
>>      hwaddr entry, kernel_load_offset;
>>      int big_endian;
>> @@ -529,7 +529,21 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
>>
>>      /* Assume that raw images are linux kernels, and ELF images are not.  */
>>      kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
>> -                           NULL, NULL, big_endian, elf_machine, 1);
>> +                           &elf_low_addr, NULL, big_endian, elf_machine, 1);
>> +    if (kernel_size > 0 && have_dtb(info)) {
>> +        /* If we have a DTB in combination with an ELF executable image,
>> +         * put the DTB at the base of RAM like we do for bootloaders.
>> +         */
>> +        uint32_t dtb_size;
>> +
>> +        if (load_dtb(info->loader_start, info, &dtb_size)) {
>> +            exit(1);
>> +        }
>> +        if (info->loader_start + dtb_size > elf_low_addr) {
>> +            fprintf(stderr, "Image %s overlaps DTB\n", info->kernel_filename);
>> +            exit(1);
>> +        }
>> +    }
>
> This shouldn't abort. The reason we need to manually check
> for overlap is because the default rom-blob behaviour of
> "overlap means don't start QEMU" isn't what we want.
> In particular, boards like virt which autogenerate DTBs
> will always have_dtb(), but we don't want to prevent
> non-DTB-aware ELF blobs from loading anywhere they like.
> The behaviour we need is "if blobs don't overlap then
> load both, otherwise load the ELF file and ignore the
> DTB".
>

OK

> (Thinking about it, that implies we either need a
> rom_del_blob() or we need to tell load_dtb() about
> areas of address space it needs to check for overlap
> with before it registers the rom blob for the dtb.)
>

... or we just call load_elf() again